Latching assembly for forklift trucks

ABSTRACT

An assembly for preventing unsupported extension of the extendible mast or slider relative to the stationary mast of a forklift truck. A coupling associated with the slider and an extendible portion of the forklift motor means automatically couples the slider to the extendible motor portion when the slider is raised relative to the stationary mast and adjacent the extendible motor portion. A latching arrangement associated with the forklift carriage and the slider functions in at least partial response to downward force on the carriage to effectively latch the carriage and slider when the slider is raised relative to the stationary mast and not adjacent the extendible motor portion.

United States Patent LATCHING ASSEMBLY FOR FORKLIFT TRUCKS 14 Claims, 9 Drawing Figs.

US. Cl.

Int. Cl

References Cited UNITED STATES PATENTS 3,221,840 12/ i965 Weinhert 8/1967 McNeeley B66b 9/20 Field of Search FOREIGN PATENTS 944,225 12/1963 Great Britain ABSTRACT: An assembly for preventing unsupported extension of the extendible mast or slider relative to the stationary mast of a forklift truck. A coupling associated with the slider and an extendible portion of the forklift motor means automatically couples the slider to the extendible motor portion when the slider is raised relative to the stationary mast and adjacent the extendible motor portion. A latching arrangement associated with the forklift carriage and the slider functions in at least partial response to downward force on the carriage to effectively latch the carriage and slider when the slider is raised relative to the stationary mast and not adjacent the extendible motor portion.

PATENIEB FEB SIHYI N 3561.568

sum 1 BF 5 I INVENTOR EUGENE E. HANSEN BY I WMZRNE s .PATENTEDFEB 91971 3,561 568 sum 2 OF 5 Q JNVENTOR EUGENE E. HANSEN ATTORNEYS PATENTED FEB 9197:

I sum 3 OF S INVENTOR EUGENE E. HANSEN E PATENIED FEB 9 l97| SHEET UF 5 I FINVENTOR EUGENE E. HANSEN JZWY PATENTEDFEH 9mm 1 3561.568

sum 5 nr 5 VENTOR EUGENE HANSEN LATCI'IING ASSEMBLY FOR FORKLIFT TRUCKS The present invention relates to lift mechanisms and more particularly to lift trucks having a stationary mast supporting an extendible mast or slider wherein means are provided to prevent unsupported extension of the slider relative to the stationary mast. Lift trucks of the type presently contemplated are provided with an extensible slider supported by the stationary mast, a carriage mounted for vertical movement upon the slider and a motor or ram for raising the carriage and slider relative to the stationary mast.

Movement of the carriage, slider and ram relative to the stationary mast and to each other for raising the carriage from ground level to its fully extended height may be considered in three stages. The carriage is first raised in free lift travel by the motor without accompanying elevation of the slider until the top of the ram approaches the top of the stationary mast and SIICIGI'.T|1C carriage and extendible mast are then both raised by the ram until the carriage approaches the top of the extended slider. During this portion of carriage elevation, the slider experiences the same rate of elevation as the ram. In the final stage of carriage elevation, the carriage and slider are raised relative to both the stationary mast and the extendible motor portion.

The problem contemplated by the present invention arises when elevation of the carriage is terminated at any point along either of its last two stages of elevation. If the carriage is then lowered, the extended slider may tend to cock or otherwise stick in an elevated position relative to the stationary mast so that upon continued descent of the carriage, the slider is relatively unsupported except for frictional engagement with the stationary mast. The extended slider is then subject to dropping suddenly and damaging portions of the mast assembly or a load supported by the carriage.

The prior art has attempted to overcome this problem by means of springs or lost motion connections between the slider and the ram, for example. Since these mechanisms are not positively acting, a condition may still arise where the slider is in a raised and unsupported position relative to the stationary mast. Various latching arrangements have also been developed to overcome this problem but tend to be complex and unreliable due to relative movement of the various components of the mast assembly during raising and lowering of the carriage along its full range of elevation.

The present invention overcomes the above problem in a mechanically simple and novel manner by means which automatically couple an extendible motor portion to the slider when the slider is raised relative to the stationary mast and traveling together with the extendible motor portion. Additional means automatically and effectively latch the carriage to the slider when the slider is in an elevated condition relative to the stationary mast and traveling at a rate different from that of the extendible motor portion.

Accordingly, it is an object to provide apparatus in a lift truck for preventing unsupported extension of its slider relative to the stationary mast.

It is another object to provide a coupling assembly suitable for use in a lift truck mast assembly for automatically coupling the slider and an extendible portion of the motor when the slider is extended from the stationary mast and adjacent the extendible motor portion.

It is also an object to provide a latching assembly for securing the carriage to the slider when the slider is extended from the stationary mast and traveling at a rate different from that of the extendible motor portion.

Other objects and advantages of the present invention are made apparent in the following description having reference to the accompanying drawings wherein:

FIG. 1 is a front view in elevation of the mast assembly for a forklift truck;

FIG. 2 is a side view in elevation of a forklift truck with parts of the mast assembly shown in section;

FIGS. 3, 4 and 5 are also front views in elevation of the mast assembly showing its carriage at different stages of elevation upon the mast assembly;

FIG. 6 is a side view in elevation, with parts in section, of a crosshead on the extendible ram of the mast assembly and includes a portion of the slider;

FIG. 7 is a plan view of the crosshead member and associated latches taken along section line VII-VII of FIG. 6;

FIG. 8 is a fragmentary view of one of the latch assemblies taken along section line VIII-VIII of FIG. 7; and

FIG. 9 is a fragmentary view of the other latch assembly taken along line IX-IX of FIG. 7.

A forklift truck is illustrated in FIG. 2 as having a mast assembly II which is also shown in FIG. I. The mast assembly includes a stationary mast comprising a pair of channeled uprights I2 and 13 supporting an extendible mast or slider assembly 14. A carriage 16 is mounted for vertical travel upon the slider 14 with a pair of forks 17 extending forwardly from the carriage in cantilevered fashion. Vertical motion of the carriage upon the slider and the slider relative to the stationary mast is effected by a motor or hydraulic ram 18 having an extendible piston 19 which is best seen in FIGS. 35. A crosshead 21 is secured to the upper end of the rod I9. A pair of flexible drive chains 22 are secured at one end to the stationary mast, trained over rotatable sprocket gears 23 secured to each side of the crosshead 21 with the other ends of the chain being secured to a lower crossmember 24 of the carriage. The slider assembly 14 has a channeled upright 26 slidably mounted upon each of the stationary mast uprights l2 and 13. A cross member 27 is secured across the tops of the slider uprights 26. The carriage assembly has an upper roller 28 and a lower roller (not shown) arranged for vertical travel in a channel 29 formed by each slider upright 26.

The manner in which the carriage is raised and lowered between ground level and fully extended height is illustrated by FIGS. 1 and 3-5. The carriage is shown at ground level in FIG. 1. As the hydraulic rod 19 is extended, the carriage 16 is drawn upwardly by the chains 22 while the position of the slider 14 is unchanged relative to the stationary mast. This portion of the carriage elevation, commonly referred to as free-lift travel" terminates as the crosshead 21 mounted on the hydraulic rod 19 approaches the slider crossmember 27. This position is illustrated in FIG. 3.

Upon continued extension of the rod 19 from the position shown in FIG. 3, the slider is carried by and raised at the same rate of travel as the crosshead 21 while the carriage continues to be drawn upwardly by the chains 22. This portion of the carriage elevation terminates as the carriage approaches the crossmember 27 at the top of the slider assembly as shown in FIG. 4.

Upon continued extension of the hydraulic rod 19 from the position of FIG. 4, a bumper 30 on the carriage engages the slider assembly so that the two are raised in unison relative to both the stationary mast and the crosshead 21. In this manner, the carriage is raised to its fully extended height as shown in FIG. 5. The carriage is lowered to ground level by the converse of the above steps.

Upward travel of the carriage may be terminated and the carriage again lowered toward ground] level at any point of extension from the position of FIG. 3 up to and including that illustrated in FIG. 5. It is apparent that, for any carriage position within that range, the slider assembly will be in an extended condition relative to the stationary mast so that binding between the slider and stationary mast, for example, would leave the slider in a relatively unsupported condition subject to sudden dropping and possible damage to the mast assembly or carriage load.

To overcome this problem, the present invention provides means for positively urging the slider assembly downwardly during descent of the carriage from any position in which the slider assembly is extended from the stationary mast. As the crosshead 21 approaches the slider crossmember 27, at the end of free lift as illustrated in FIG. 3, a coupling 31 automatically locks those members together during the extent of their travel in unison between the position illustrated in FIGS. 3 and 4. As the carriage approaches the position illustrated in FIG. 4, an unlatching assembly 33, mounted upon the crosshead 21 and carriage 16 and illustrated in FIGS. 6, 7 and 8, causes the coupling 31 to be unlocked and permits upward travel of the slider 14 and its crossmember 27 relative to the crosshead 21 toward the position shown in FIG. 5.

As the carriage is lowered toward the position illustrated in FIG. 3, another unlatching assembly 32, mounted upon the slider crossmember 27 and shown in FIGS. 6, 7 and 9, causes the coupling 31 to unlock the crosshead 21 from the slider 14 and permits the crosshead 21 to descend to the position shown in FIG. 1.

Since the slider crossmember 27 is traveling in an extended condition relative to the crosshead 21 between the position shown in FIGS. 4 and 5, the coupling 31 is ineffective to exert a constant and positive downward force upon the slider during its descent within that range. During that portion of travel, latching means indicated at 34 in FIG. 2 are effective to exert a positive downward force upon the slider assembly during descent of the carriage. The coupling 31, the unlatching assemblies 32 and 33 and the latching means 34 are described in greater detail below.

The manner in which the coupling 31 automatically locks the crosshead 21 to the slider crossmember 27 while they are in contact with each other is best described with reference to FIG. 6. A tubular member 36 is secured by means of a pin 38 to a retainer 37 mounted on the crossmember 27 and extends downwardly for axial and concentric alignment with a cylindrical member 39 threaded into the crosshead 21. A guide rod 41 is also secured to the crossmember 27 by means of the pin 38 and extends downwardly through a central bore 42 fonned in the cylindrical member 39 and the crosshead 21 to maintain the axial and concentric alignment between the tubular member 36 and the cylindrical member 39. The tubular member 36 defines a plurality of circumferentially spaced apertures, one of which is indicated at 43, while the cylindrical member 39 is formed with an annular groove 44.

Means for locking the tubular member 36 to the cylindrical member 39 and accordingly locking the crossmember 27 to the crosshead 21 comprises a ball 46 disposed within each of the apertures 43 and having a radial dimension or diameter which is greater than the depth of the aperture but not more than the combined depth of the aperture 43 and the groove 44. As the crosshead 21 approaches into engagement with the crossmember 27, which condition is illustrated by the carriage position in FIG. 3, the balls 46 are urged into locking relation between the tubular member 36 and cylindrical member 39 by means of an outer sleeve 47 suspended from the tubular member 36 and urged downwardly by means of a spring 48. Downward travel of the sleeve 47 relative to the tubular memlmer 36 is limited by means of a wire ring 49. A cam follower plate 51 is secured to the outer sleeve 47 and extends outwardly in a radial fashion to overlap a cam plate 52 secured to the top of the crosshead 21 as by screws 53.

Referring also to FIG. 7, the cam follower plate 51 defines a plurality of radially shaped slots 54 which are in equal circumferential spacing with radially shaped earns 56 mounted upon the cam plate 52. The cams 56 are formed with ramp surfaces 57 as best seen in FIG. 6. A spring connected at 59 to the retainer 37 and to a projection 61 of the cam follower plate 51 (see FIG. 7) urges the cam follower plate 51 in a clockwise direction so that the slots 54 are in alignment with the cams 56 and the cam follower plate 51 is fiush with the cam plate 52 as seen in FIG. 6 under the influence of the spring 48. In this manner, the outer sleeve 47 is permitted to drop under the influence of the spring 48 and urges the balls 46 into locking engagement between the tubular member 36 and the cylindrical member 39. A more complete description of the coupling mechanism is presented below with the discussion of the second unlatching assembly 32.

The unlatching assemblies 32 and 33 serve to uncouple the crosshead 21 from the crossmember 27 upon descent of the carriage past the position illustrated in FIG. 3 and upon elevation of the carriage past the position illustrated in FIG. 4, respectively. To first describe the unlatching assembly 32,

having reference to FIGS. 6, 7 and 9, a bellcrank 62 is pivoted to the slider crossmember 27 generally in line with the rear of the crosshead 21. A bracket 63 is mounted on the stationary mast to engage a roller 64 secured to one arm 66 of the bellcrank 62 as the slider descends with the carriage toward the position illustrated in FIG. 3. As the bellcrank is actuated by engagement of the bracket 63, the other bellcrank arm 67 engages a pin 68 and causes counterclockwise rotation of the cam follower plate 51 (see FIG. 7). Movement of the pin 68 to I its position indicated in FIG. 9 at 68 causes the cam follower plate 51 to ride up on the ramp surfaces 57 of the cams 56. Referring particularly to FIG. 6, this rising motion of the cam follower plate 51 urges the outer sleeve 47 upwardly against the spring 48 and permits the balls 46 to move radially outwardly from locking engagement with the surface indentations 44 in the cylindrical member 39. In this manner, the tubular member 36 and cylindrical member 39 are uncoupled and the crosshead 21 may descend relative to the slider crossmember 27 toward its position shown in FIG. 1.

As the carriage is again raised toward its position illustrated in FIG. 3 the crosshead 21 moves upward and as the cylindrical member 39 comes in contact with inner sleeve 91 it is moved upward until it contacts wire ring 93. Sleeve 47 cannot drop down as it is being held up by roller 64 on lever 66 in contact with the bracket 63 on mast. When crosshead 21 moves slider 27 in upward direction roller 64 moves away from bracket 63. Spring 69 allows lever 67 to return to position shown in FIG. 9. Cam follower 51 will then move in a clockwise rotation thus allowing sleeve 47 to drop and lock crosshead 21 to slider 27.

The construction and operation of the unlatching assembly 33 may best be seen with reference to FIGS. 6, 7 and 8. A bellcranklike member 72 having two angularly fixed anns 73 and 74 is pivoted to the front of the crosshead 21. A lever 76 is pivoted to the rear of the carriage in offset relation from the bellcrank 72. A flange 77 extends outwardly from the lever 76 for engagement with a roller 78 mounted on the bellcrank arm 73. The lever is positioned upon the carriage so that as the carriage is elevated toward the position illustrated in FIG. 4, the flange 77 engages the roller 78 and pivots the bellcrank arm 74 against a pin 79 secured to the extension 61 of the cam follower plate 51 (see FIG. 6). Pivoting of the bellcrank arm 74 against the pin 79 causes counterclockwise rotation of the cam follower plate 51 which unlocks the tubular member 36 from the cylindrical member 39 in a manner similar to that described above for the unlatching assembly 22. The slider crossmember 27 is accordingly freed for upward extension from the crosshead 21 toward the position illustrated in FIG. 5.

As the carriage is elevated from the position shown in FIG. 4, the roller 78 on the bellcrank 72 rides off the lever flange 77 and the lever 76 if elevated above the bellcrank 72 along with the carriage. As the bellcrank roller rides off the flange, it is returned to its original position against a stop 81 by means of a spring 82 which is connected at 83 to the crosshead 21. As the carriage is elevated past the position illustrated in FIG. 4, an arm 84 on the lever 76 opposite its flange 77 engages a stop 86 mounted on the carriage which supports the lever as it actuates the bellcrank 72. As the carriage is lowered past the position illustrated in FIG. 4, the roller 78 engages the under surface of the flange 77 and pivots the lever 76 away from the stop 86 so that the position of the bellcrank is not effected.

As the lever 76 passes the bellcrank 72 and the bellcrank is returned to its original position, the cam follower plate 51 is rotated back to its original locked position by the spring 58. Having particular reference to FIG. 6, upon descent of the carriage from a position above that shown in FIG. 4 the outer sleeve 47 is otherwise free to be urged downwardly by the spring 48. To prevent the outer sleeve 47 from dropping into its locking position while the slider crossmember is raised away from the crosshead 21, an inner sleeve 91 is suspended within the tubular member 36 and is urged downwardly by'a spring 92. Downward travel of the inner sleeve 91 is limited by a wire ring 93 mounted upon the inner surface of the tubular member 36. As the coupling is unlocked at the carriage position illustrated in FIG. 4, the tubular member 36 commences to rise away from the cylindrical member 39. The inner sleeve 91 is urged downwardly by the spring 92 to remain in contact with the cylindrical member 39 until it is in overlapping relation with the apertures 43. In this manner, the balls 46 cannot be forced inwardly of the apertures 43 and the outer sleeve 47 remains in its raised position.

As the slider crossmember again descends toward the position illustrated in FIG. 4, the inner sleeve 91 is urged upwardly against the spring 92 by the cylindrical member 39 so that it does not interfere with reengagement of the blocking ball 46 within the groove 44 of the cylindrical member.

The coupling 31 described above is effective to positively prevent unsupported extension of the slider when the carriage descends from any position intermediate those shown in FIGS. 3 and 4. Within that range, the slider is extended from the stationary mast and traveling at the same rate as the crosshead 21.

Referring to FIG. 5, the coupling 31 is not effective to perform the same function while the slider crossmember 27 is raised away from the crosshead 21. During this portion of carriage travel the latching mechanism indicated at 24 in FIG. 2 effectively locks the carriage to the slider so that upon descent of the carriage from any position between those illustrated in FIGS. 4 and 5, the slider is positively drawn down along with the carriage until it reaches the position of FIG. 4 and is again coupled to the crosshead 21.

The latching means 34 comprises a notch formed at the top of each slider upright 26 and along the forward surface of the channel 29. As the carriage is raised to the position illustrated in FIG. 5, a load on the cantilevered forks 17 of the carriage urges the upper carriage rollers 28 into engagement with the notches 34. The position of the rollers, with the carriage in the position illustrated in FIG. 5, is indicated in broken lines at 28' in FIG. 2.

Engagement of the rollers 28 with the notches 34 may be effected by the weight of the carriage alone. However, since damage is most likely to result when the carriage is loaded, the present latching arrangement is particularly effective in response to a load carried upon the forks 17 of the carriage. As the carriage descends from the position of FIG. 5, the rollers have a tendency to rotate clockwise (as seen in FIG. 2) and climb out of the notches 34. However the forward load on the carriage maintains the rollers within the notches until the carriage reaches the position illustrated in FIG. 4. At that point, the slider assembly is locked to the crosshead 21, and it is prevented from moving downwardly with the carriage. Since the slider now moves downwardly with the crosshead which is descending at a slower rate than the carriage, the rollers are forced out of the notches 34. The carriage is thus free to descend toward the position illustrated in FIG. 3.

Thus the coupling 31 and the latching notches 34 are effective in unison to positively preventunsupported extension of the slider from the stationary mast while the carriage is descending from any position along its full range of travel.

Iclaim: I

1. In an industrial machine of the type having a stationary mast, an extendible mast mounted for vertical travel along the stationary mast, a carriage mounted for vertical travel along the extendible mast and a motor for controlling travel of the carriage along the extendible mast and travel of the carriage and extendible mast along the stationary mast, the combination comprising:

means for effectively coupling the extendiblemast with a portion of the motor when the extendible mast is raised relative to the stationary mast and traveling at the same rate as the motor portion, and

means for effectively latching the carriage to the extendible mast in at least partial response to downward force on the carriage when the extendible mast is raised relative to the stationary mast and traveling at a rate difierent from that of the motor portion, the latching means comprising a roller secured generally at the rear of the carriage and arranged for travel travel along a channel at least partially defined by the extendible mast and means formed by the extendible mast forwardly of the channel for receiving the roller, the receiving means being a notch formed forwardly of the channel and generally at the top of the extendible mast.

2. The invention of claim I wherein the motor has a vertically extendible portion and flexible means are trained generally over the extendible portion for connection to the carriage, extension of the extendible motor portion beyond the limit of its simultaneous travel with the extendible mast tending to urge the carriage member toward the receiving means of the extendible mast.

3. The invention of claim 2 wherein the motor is a hydraulic cylinder, the extendible motor portion is the rod of the cylinder with a crosshead secured at the upper end of the rod and the flexible means comprise a pair of chains each secured at one end to the stationary mast and trained over sprockets on the crosshead for connection to the carriage.

4. In an industrial machine of the type having a stationary mast, an extendible mast mounted for vertical travel along the stationary mast, a carriage mounted for vertical travel along the extendible mast and a motor having; an upwardly extendible portion for controlling travel of the carriage along the extendible mast and travel of the carriage and extendible mast along the stationary mast, the combination comprising:

means for effectively coupling the extendible mast with a portion of the motor when the extendible mast is raised relative to the stationary mast and traveling at the same rate as the motor portion, the coupling means comprising a pair of vertically aligned members affixed respectively to the extendible motor portion and extendible mast, means for coupling and uncoupling the coupling members, one of the coupling members including a tubular member and the other coupling member including a cylindrical member in axial alignment with the tubular member and having an outside diameter slightly smaller than the inside diameter of the tubular member, a locking element capable of preventing relative axial motion of the tubular and cylindrical members and means for selectively urging the locking element into locking engagement between the tubular and cylindrical members; and

means for effectively latching the carriage to the extendible mast in at least partial response to downward force on the carriage when the extendible mast is raised relative to the stationary mast and traveling at a rate different from that of the motor portion.

5. The invention of claim 4 wherein the last said means are effective to normally cause locking engagement of the tubular and cylindrical members and to release the locking element from engagement therebetween as the extendible motor portion and extendible mast approach a limit of travel beyond which they tend to separate.

6. The invention of claim 4 wherein the tubular member is mounted on a crossmember generally at the top of the extendible mast and the cylindrical member is mounted on a crosshead at the top of the extendible motor portion, the tubular member defining an aperture and the cylindrical member defining a circumferential groove, the locking element being arranged within the aperture and having a radial dimension greater than the depth of the aperture and less than the depth of the aperture and groove combined.

7. The invention of claim 6 wherein the locking element is urged into engagement between the tubular and cylindrical members by an outer sleeve carried on the tubular member and normally urged toward a downward axial limit so that its inner surface is generally flush with the outside diameter of the tubular member adjacent the aperture.

8. The invention of claim 7, further comprising an annular ring secured to the outer sleeve and forming circumferentially spaced slots, cam members circumferentially spaced upon the top of the crosshead and forming ramp surfaces relative to the top of the crosshead, and means for urging the slots of the annular ring into angular alignment with the respective cam members 9. The invention of claim 8 further comprising unlocking elements which include lever means associated with the annular ring for rotating the ring on the ramp surfaces of the cam and raising the outer sleeve to release the coupling members from each other and elements arranged respectively at the top of the stationary mast and on the carriage for actuating the lever means.

10. The invention of claim 9 wherein one of the levers is a bellcrank arranged on the extendible mast crossmember rearwardly of the crosshead with the associated actuating element being on the stationary mast, another lever being a bellcrank arranged on the front of the crosshead with the associated actuating element being at the rear of the carriage, and further comprising lost motion means for permitting downward passage of the actuating element on the carriage relative to the other lever without varying the angular position of the annular ring. I

ll. The invention of claim 7, further comprising an inner sleeve being urged downwardly relative to the tubular member to have a surface generally flush with the aperture when the tubular member is uncoupled from the cylindrical member.

12. An assembly suitable for coupling an extendible motor portion to an extendible mast when the extendible motor portion and extendible mast are traveling at the same rate of speed relative to a stationary mast upon which they are mounted, comprising:

a cylindrical member;

a tubular member maintained in axial and concentric alignment with the cylindrical member;

a locking element capable of positively preventing relative axial motion of the tubular and cylindrical members and means for selectively urging the locking element into locking engagement with the tubular and cylindrical members; and

the cylindrical member and tubular member being vertically mounted on the extendible motor portion and a crossmember at the top-of the extendible mast respectively, 'the tubular member defining an aperture and the cylindrical member defining a circumferential groove, the locking element being arranged within the aperture and having a radial dimension greater than the depth of the aperture and less than the combined depth of the aperture and groove.

13. The invention of claim 12 further comprising an annular ring secured to the outer sleeve and forming circumferentially spaced slots, cam members circumferentially spaced upon the top of the crosshead and forming ramp surfaces relative to the top of the crosshead, and means for urging the slots of the annular ring into angular alignment with the respective cam members, unlocking elements which include lever means associated with the annular ring for rotating the ring on the ramp surfaces of the cam and raising the outer sleeve to release the coupling members from each other and elements arranged respectively at the top of the stationary mast and on the carriage for actuating the lever means.

14. The invention of claim 13 further comprising an inner sleeve being urged downwardly relative to the tubular member to have a surface generally flush with the aperture when the tubular member is uncoupled and separated from the cylindrical member. 

1. In an industrial machine of the type having a stationary mast, an extendible mast mounted for vertical travel along the stationary mast, a carriage mounted for vertical travel along the extendible mast and a motor for controlling travel of the carriage along the extendible mast and travel of the carriage and extendible mast along the stationary mast, the combination comprising: means for effectively coupling the extendible mast with a portion of the motor when the extendible mast is raised relative to the stationary mast and traveling at the same rate as the motor portion, and means for effectively latching the carriage to the extendible mast in at least partial response to downward force on the carriage when the extendible mast is raised relative to the stationary mast and traveling at a rate different from that of the motor portion, the latching means comprising a roller secured generally at the rear of the carriage and arranged for travel travel along a channel at least partially defined by the extendible mast and means formed by the extendible mast forwardly of the channel for receiving the roller, the receiving means being a notch formed forwardly of the channel and generally at the top of the extendible mast.
 2. The invention of claim 1 wherein the motor has a vertically extendible portion and flexible means are trained generally over the extendible portion for connection to the carriage, extension of the extendible motor portion beyond the limit of its simultaneous travel with the extendible mast tending to urge the carriage member toward the receiving means of the extendible mast.
 3. The invention of claim 2 wherein the motor is a hydraulic cylinder, the extendible motor portion is the rod of the cylinder with a crosshead secured at the upper end of the rod and the flexible means comprise a pair of chains each secured at one end to the stationary mast and trained over sprockets on the crosshead for connection to the carriage.
 4. In an industrial machine of the type having a stationary mast, an extendible mast mounted for vertical travel along the stationary mast, a carriage mounted for vertical travel along the extendible mast and a motor having an upwardly extendible portion for controlling travel of the carriage along the extendible mast and traVel of the carriage and extendible mast along the stationary mast, the combination comprising: means for effectively coupling the extendible mast with a portion of the motor when the extendible mast is raised relative to the stationary mast and traveling at the same rate as the motor portion, the coupling means comprising a pair of vertically aligned members affixed respectively to the extendible motor portion and extendible mast, means for coupling and uncoupling the coupling members, one of the coupling members including a tubular member and the other coupling member including a cylindrical member in axial alignment with the tubular member and having an outside diameter slightly smaller than the inside diameter of the tubular member, a locking element capable of preventing relative axial motion of the tubular and cylindrical members and means for selectively urging the locking element into locking engagement between the tubular and cylindrical members; and means for effectively latching the carriage to the extendible mast in at least partial response to downward force on the carriage when the extendible mast is raised relative to the stationary mast and traveling at a rate different from that of the motor portion.
 5. The invention of claim 4 wherein the last said means are effective to normally cause locking engagement of the tubular and cylindrical members and to release the locking element from engagement therebetween as the extendible motor portion and extendible mast approach a limit of travel beyond which they tend to separate.
 6. The invention of claim 4 wherein the tubular member is mounted on a crossmember generally at the top of the extendible mast and the cylindrical member is mounted on a crosshead at the top of the extendible motor portion, the tubular member defining an aperture and the cylindrical member defining a circumferential groove, the locking element being arranged within the aperture and having a radial dimension greater than the depth of the aperture and less than the depth of the aperture and groove combined.
 7. The invention of claim 6 wherein the locking element is urged into engagement between the tubular and cylindrical members by an outer sleeve carried on the tubular member and normally urged toward a downward axial limit so that its inner surface is generally flush with the outside diameter of the tubular member adjacent the aperture.
 8. The invention of claim 7, further comprising an annular ring secured to the outer sleeve and forming circumferentially spaced slots, cam members circumferentially spaced upon the top of the crosshead and forming ramp surfaces relative to the top of the crosshead, and means for urging the slots of the annular ring into angular alignment with the respective cam members.
 9. The invention of claim 8 further comprising unlocking elements which include lever means associated with the annular ring for rotating the ring on the ramp surfaces of the cam and raising the outer sleeve to release the coupling members from each other and elements arranged respectively at the top of the stationary mast and on the carriage for actuating the lever means.
 10. The invention of claim 9 wherein one of the levers is a bellcrank arranged on the extendible mast crossmember rearwardly of the crosshead with the associated actuating element being on the stationary mast, another lever being a bellcrank arranged on the front of the crosshead with the associated actuating element being at the rear of the carriage, and further comprising lost motion means for permitting downward passage of the actuating element on the carriage relative to the other lever without varying the angular position of the annular ring.
 11. The invention of claim 7, further comprising an inner sleeve being urged downwardly relative to the tubular member to have a surface generally flush with the aperture when the tubular member is uncoupled from the cylindrical member.
 12. An assembly suitable for coupling an extendible motOr portion to an extendible mast when the extendible motor portion and extendible mast are traveling at the same rate of speed relative to a stationary mast upon which they are mounted, comprising: a cylindrical member; a tubular member maintained in axial and concentric alignment with the cylindrical member; a locking element capable of positively preventing relative axial motion of the tubular and cylindrical members and means for selectively urging the locking element into locking engagement with the tubular and cylindrical members; and the cylindrical member and tubular member being vertically mounted on the extendible motor portion and a crossmember at the top of the extendible mast respectively, the tubular member defining an aperture and the cylindrical member defining a circumferential groove, the locking element being arranged within the aperture and having a radial dimension greater than the depth of the aperture and less than the combined depth of the aperture and groove.
 13. The invention of claim 12 further comprising an annular ring secured to the outer sleeve and forming circumferentially spaced slots, cam members circumferentially spaced upon the top of the crosshead and forming ramp surfaces relative to the top of the crosshead, and means for urging the slots of the annular ring into angular alignment with the respective cam members, unlocking elements which include lever means associated with the annular ring for rotating the ring on the ramp surfaces of the cam and raising the outer sleeve to release the coupling members from each other and elements arranged respectively at the top of the stationary mast and on the carriage for actuating the lever means.
 14. The invention of claim 13 further comprising an inner sleeve being urged downwardly relative to the tubular member to have a surface generally flush with the aperture when the tubular member is uncoupled and separated from the cylindrical member. 